1. Field of the Invention
The present invention relates to the field of devices for packaging carbon dioxide snow inside a plastic film.
2. Related Art
It is known that frozen, deep-frozen or even fresh products, notably foodstuffs, which have to be kept at a controlled temperature of +2° C. to −20° C., or even less, with no break in their cold chain from the time that they are cooled, frozen or deep-frozen to the time of their use, require warehouses, means of transport and stores which are fitted with refrigeration installations, which at the present day are generally electric. However, in many cases, it is impossible to transport the products without removing them from the refrigeration installation in which they are being stored, and the risks of a rise in temperature are then great, particularly if the climatic conditions are unfavorable. In order to avoid such a rise in temperature during their transport, it is common practice for such products to be placed in an environment that is kept at a controlled temperature in an isothermal chamber. Temperature regulation is ensured for example by slow sublimation of carbon dioxide snow packaged in bags made of perforated plastic film. Carbon dioxide snow is a relatively inexpensive product which has an attractive refrigeration value: 573 kJ/kg of snow. Its temperature of around −80° C. ensures that the products can be kept cold for relatively lengthy periods.
By way of illustration, reference may be made to document EP-1 186 842 which describes a device for automatically and continuously packaging carbon dioxide snow in a plastic film.
Reference may also be made to documents FR-2 604 243 or EP-823 600, or even to U.S. Pat. No. 5,271,233 which describe cooling blocks containing a mass of carbon dioxide snow.
Reference may also be made to document EP-1 090 259, which describes a method and an installation for obtaining cooling blocks made up of a wrapper made of a porous material (capable of withstanding low temperatures of below 1° C.) containing a mass of carbon dioxide snow enclosed and contained in the wrapper, the wrapper being made of a material which, as this document indicates, has a “porosity to air of between 100 and 500 m3/m2/mn for an air pressure of the order of 196 Pa”, for example made of a nonwoven polypropylene.
A manual bagging machine is therefore a piece of equipment which, using a source of liquid CO2, can be used, by expansion, to generate carbon dioxide snow directly in bags made of a porous material (generally woven polypropylene). The amount of snow can be adapted according to the injection time used, and according to the supply pressure of the liquid CO2. The equipment available on the market generally seeks to be able to fill several bags simultaneously.
The injectors installed on the manual bagging machines available are usually formed of perforated tubes.
By way of example, as schematically illustrated in the attached FIG. 1 which relates to the prior art, a feed tube, connected at its upstream part to a source of liquid CO2, feeds a set of injection pipes, each facing a cell in which a bag that is to be filled will be positioned, and each connected at its upstream part to an electrically operated valve (directly or alternatively via primary tubes to which they are welded).
Each injection pipe has an injection orifice machined along its length, and it will therefore be appreciated that, in order to change the injection delivery rate, it was necessary to remove one or more of the injection pipes and modify (remachine) the injection orifice, something which represents a complicated exercise offering little flexibility.
This configuration of the prior art did, on the other hand, ensure perfect rigidity, something which is needed for comfortably introducing the bags and for removing the bags.